1. Field of the Invention
The present invention relates to an antenna device and more particularly to the antenna device that can operate in a plurality of bands (transmitting/receiving bands) and a multi-band wireless communication apparatus using the antenna device.
2. Description of the Related Art
In recent years, a wireless communication apparatus such as a mobile phone or a like has become widespread and various bands are used in communications. In a recently-available mobile phone called a dual-band, triple-band, or quad-band type mobile phone in particular, one mobile phone is made to operate in a plurality of bands (transmitting/receiving bands). In such a circumstance, hurried development of an antenna device making up antenna circuits that can be embedded in a mobile phone or a like being capable of operating in a plurality of bands (transmitting/receiving bands) described above is needed. It is thus necessary that, in order to respond to needs for further miniaturization of a wireless communication apparatus such as a mobile phone and for operations in multi-bands, despite a tendency of an increase in antenna components, the antenna device not only can achieve its miniaturization but also can have high performance.
An example of such a conventional antenna device mounted on one wireless communication apparatus such as a mobile phone which can operate in a plurality of bands is disclosed in, for example, Patent Reference 1 (Japanese Patent Application Laid-open No. 2004-363789) in which a dielectric antenna portion having a radiation electrode pattern and a plate antenna portion make up an inverted F antenna. Also, an antenna device is disclosed in Patent Reference 2 (Japanese Patent Application Laid-open No. 2004-7803) in which a conductive plate-shaped auxiliary element is attached to a dielectric antenna portion with a radiation electrode pattern. Another antenna device is disclosed in Patent Reference 3 (International Publication No. WO 99/28990) in which an inverted F antenna is constructed by arranging a dielectric between a radiation conductor and a grounding conductor. Still another antenna device made up of only a dielectric is disclosed in Patent Reference 4 (Japanese Patent Application Laid-open No. 2005-229365). Yet another antenna device is disclosed in Patent Reference 5 (Japanese Patent Application Laid-open No. Hei 3-502157) in which a dielectric core is mounted in a loop of a loop antenna.
However, the conventional antenna devices disclosed in the Patent References 1 and 2 have a problem in that fine adjustments are not easy since their impedance matching is performed by using the radiation electrode patterns formed on the dielectric antenna portion. The antenna device disclosed in the Patent Reference 3 has also a problem in that a bandwidth is made narrow and radiation efficiency is lowered since the dielectric is placed between the radiation conductor and a grounding conductor. The antenna device disclosed in the Patent Reference 4 has also a problem in that the radiation efficiency and sensitivity are lowered when compared with the antenna devices disclosed in the Patent References 1, 2, and 3. The antenna device disclosed in the Patent Reference 4 has another problem that an antenna needs to be installed for every band and space for the antenna device is greatly occupied by antenna circuits and its antenna gain is reduced due to fluctuations of directivity of the antenna and degradation in VSWR (Voltage Standing Wave Ratio) caused by interactions among the installed antennas for each band. The antenna device disclosed in the Patent Reference 5 has a problem that the antenna used is a single loop antenna in which its line length or electrical length consists of one wavelength and, therefore, space for the antenna is greatly occupied in the antenna device.